As a Turkish boy from Iran, I’d suggest my own city, Tabriz. It’s a mountainous city in North West Iran with mild weather and good ancient places.
El-goli, Bazar and Blue masque are the famous ancient places. I have been to the most beautiful city in Iran. I mean Shiraz, which has a lot of historical buildings. You may have heard about Persepolis, which was built about 2500 years ago. This place was a capital of Achaemenid dynasty which was the first empire in the history. There is another ancient city, Istahan. The first Polo arena in history is Imam square where 2500 years ago Persians used to play there.
All in all, despite the negative perception, it is safe for foreigners to see Iran and they are all welcome! Looking forward to seeing you in Iran!